Sound-absobbing plasteb



Patented June 12, 1923.

1,458,631 PATENT OFFICE.

PAUL E. SABINE, OF GENEVA, ILLINOIS, ASSIGNOR OF ONE-HALF TO RIVERBANK LABORATORIES, OF GENEVA, ILLINOIS.

SOUND-ABSORBING PLASTER,

Application filed April 29, 1921. Serial No. 485,372.

To all whom it may concem:

Be it known that I, PAUL E. SABINE, a citizen of the United States, residin at Geneva, in the county of Kane and 'tate of Illinois, have invented certain new and useful Improvements in Sound-Absorbing Plaster, of which the following is a specification.

This invention relates and application of a special laster of such nature that it may be applie to walls, cellings, or the like, with ordlnary, plastering tools, and when set or hardened W111 have the property of absorbing sound to a much greater degree than plasters heretofore known.

' As is well known it is oftentimes a ques tion of considerable im rtance and necessity to so construct buildings, rooms, and the like, as to reduce to the minimum the penetration thereinto of audiblesound waves. The necessit for this more often occurs in such buil ings as auditoriums, concert halls, theaters, and the like, where it is of prime importance to secure proper acoustical conditions and to reduce the noise thereinfrom external sources.

It has been long known that orous surfaces have the property of a rbing a large percentage of the sound that me be incident upon them, and'various meth s of securin structural materials possessing porosity ave been devised. 'In actual practice, however, none of these materials can be applied as plaster to thewalls, ceilings, and the like, since it has heretofore been impossible to produce a mortar of such conto the preparation sistency and nature that it can be-handled with plastering tools, and which will set into a porous body. Porosity has heretofore been secured body material which the finest or removed, and

'bondin curs on y at. the

leave inter-communicating out the, body of the har ened material.

Actual ex eriment, however, shows that a mixture 0 this character cannot be applied as a plastic material, since the 163l1l81t8 porosit calls for a mixture too ry to ban ed as ordinary-mortar or plaster.

Among the objects of my invention are a granular substance, from particles have been screened such a small percentage of points of contact, so as to ;break in the setting of the plaster, giving ther' to make.

by using as an aggregate ormaterial used that cementing 'oc-- res throug'hpa to provide a plaster of such nature that it may be applied to walls, ceilings, and the hke, with ordinary plastering tools, and which when hardened will a greater degree than possible with the plasters heretofore known; further the proper-choice of materials and the method absorb sound to" e separate material of such nature that the voids between the body particles are not completely filled in the process of trowelling and finishing but the a porous and cellular, structure; further the provision of a bonding material which will form elastic surface films so that in mixing with the aggregate a large number of minute air particles are formed, which a cellularand porous nature to the hardened product further to produce a laster in which the aggregate consists o "particles having a large number of more or less sharp projections to promote porosity between the various particles;,further to provide a novel bonding'material for the aggregate; furs. ssible a more simple, highly efiicacious an cheaper produced plaster for absorbing sound; and such further objects,

advanta es and capabilities as will later -more fu 13 appear.

While I have shown in the accompanyin drawings, certain forms of aggregate, I Wish it to be understood that the same is illustrative only, and not to be considered bonding materialtherein is of as limiting the scope of my invention, since other forms of aggregate may be used.

In the drawings:

Fig. 1 shows in separated relation various 10o rtlcles .of aggregate having a large num-v 'ber of sharp projections.

Fig. 2 is a cross section showing how the I irregularl shaped particles of aggregate prevent c ose packing and form air spaces therebetween prior material added thereto.

to having the bonding- Fig. 2" isa view similar to Fig. 2, but

showing in magnified form the bonding of curves the results of careful scientific tests made to determine the efliciency of my improved plaster as a sound absorbent.

or a bonding material, I use a well known material known as Sorel cement, consisting of a mixture of a solution of magnesium chloride and magnesium oxide. When mixed to form a paste, these materials will harden into an extremely hard and tenacious solid. There are other known methods of producing the compound thus formed,- by the use of other salts of magnesium, of which I may avail without departing from the spirit of my invention. To the solution of magnesium chloride is added a very small amount of glue, gelatine, or other material, which with water will form a colloidal solution. One per cent by weight of glue is sufiicient for the purpose. The addition of even this small amount of colloidal material is of importance in securing thede sired result. The presence of the glue or other colloidal material causes a marked foaming action in the mixing of the mortar.

This action produces a wet mixture of the" proper consistency to be handled with plastering tools, and yields a hardened product sufiiciently porous to be highly absorbent of sound.

As an aggregate, I preferably use the ranulated slag from iron blast furnaces. his material is prepared .by passing the molten slag from the furnace directly into cold water. The expansive force of the steam thus formed, breaks the slag into small particles, and the cellular structure of the slag is such that these particles have each numerous sharp projecting points. Figure 1 represents the character of these particles, which are designated at 1. The advantage of this material lies in the-fact that the shapes of the particles render close packing impossible, and allows liberal intervening spaces which are filled with the porous bonding material produced as heretofore described, the whole constituting a hard porous material'which is highly absorbent of sound. While I have mentioned granulated slag, I wish any other material of such shape and nature as to accomplish the results desired, to be understood as falling within the scope of my invention.

As an instance of the employment of the foregoing materials, the following example of t eir use in the preparation of a sound absorbing plaster is given. I

To a solution in water of magnesium chloride of density 20 Baum, is added 1% by weight of glue Equal volumes of another definite fraction absorbed,

eases;

the resulting mixture and dry magnesium ingredients such asare ordinarily used in plasters would give a mixture entirely too poor in bonding material to adhere to a wall or ceiling. In mixing this product, the sharp particles of the slag, acting upon the slightly gelatinous paste produces a large number of minute air bubbles throughout the mixture. The effect is similar to that produced by beating the white of an egg. The presence of these bubbles accomplishes a two fold' purpose. It imparts to the wet mixture the proper consistency for handling, and to'the hardened product both a porous and cellular structure which renders it-highly sound absorbent. The character of the slag particles is also important, since without the projecting points, the particles would tend to pack more closely, thus counteracting the eflect just described.

en a train of sound waves is incident upon a reflecting surface, a certain'definite fraction of this incident energy is reflected, and the remainder is transmitted. For fairly rigid massive walls the fraction transmitted is small in comparison with that reflected and absorbed so that for practical purposes the sum of the reflected and absorbed sound energies'is equal to the incident energy. The

depends only upon the pitch of the sound and the nature of the surface. (See Rayleigh-Theory of Sound, Vol. II, page 332 and following (1896)).

Careful scientific tests have been made to determine the efiiciency of this material as a sound absorbent. The results of these tests are shown in Figure 3. The :ibscissae are the notes ranging from the second octave below middle C to the fourth octave above middle C. The ordinates arethe per cents of sound absorbed. Curve 1 represents the absorption of a surface of two coats of this product made as described above and applied by a journeyman plasterer to a wall composed of gypsum b ock. Curve 2 represents the percentage of sound energ absorbed by two coats of the same materia applied to a scratch coat of brown plaster upon metal lath. Curve 3 representsthe abso tion of sound by a wall finished with a bar surface of ordinary gypsum plaster.

Having now described my invention, I claim a 1. A sound absorbent plaster for walls, ceilings, and the like, comprising granular particles of irregular sha e to prevent close packing and leave voids t erebetween, and a bonding material of such nature as to not completely fill the voids between said part1- cles, said plaster beingcapable of application directly to a wall, ceiling, or the like with ordinar plastering tools. 2. A soun absorbent plaster for walls, ceilings, and the like, comprising granular particles having a large number of sharp projecting points, and a bonding material of such nature as to not completel fill the voids between said particles, said p aster being capable of application directly to a wall, ceiling, or the like with ordinary plastering tools.

3. A sound absorbent plaster for walls, ceilings, and the like, comprising granular particles of irregular shape to prevent close packing and leave voids therebetween, and a bonding material of such nature as to not completelyfill the voids between said particles, said plaster bein capable of a plication directly to a wal ceilin or t e like with ordinary plastering too s, and when hardened will absorb more than twelve per cent ofsound lying in the range of pitch between middle C and thefourth octave above middle C, when applied in thicknesses of one half inch o more.

4. .A sound absorbent plaster comprising granular particles of irregular shape, and a bonding material which when being mixed with said granular particles forms a large number of minute bubbles throughout the mixture, to permit the same to be applied as a plaster to Walls, ceilings and the'like and set into a hard ing the property 0 twelve per cent of sound 1 of pitch between middle absorbing more than ing in the range and the fourth octave above middle C, when applied in Y thicknesses of one half inch or more.

5. A sound absorbent plaster comprising granular particles having sharp projecting porous product possessas a plaster to walls, ceilings and the like and set into a hard porous product possess be applied I ing the property of absorbing more than twelve per cent of sound lving in the range of pitch between middle C and the fourth octave above middle C, when applied in thicknesses of one half inch or more.

6. A sound absorbing plaster comprising body particles of granulated slag, a bonding material consisting of the product of reaction between magnesium oxide and a solution of magnesium chloride to which is added a small per cent of a substance of colloidal nature, so that said plaster may be applied 'in a plastic condition to walls, ceilings and the like, and when hardened will be porous and capable of absorbing more than twelve per cent of sound lying in the range of pitch from middle C to the fourth octave above middle 0.

7. A plaster of the character described comprising granulated slag, and a bonding material consisting of the product of reaction between magnesium oxide and a solution of magnesium chloride to which is added a small percentage of a substance of colloidal nature, whereby the structure of the plaste .is porous and sound absorbing.

8. A plaster of the character described comprising granulated slag, and a bonding material consisting of the product of reaction between magnesium oxide and a solution of magnesium chloride to which is added a small percentage of a elatinous material, whereby the structure of the plaster is porous and sound absorbing.

In witness whereof, I hereunto subscribe my name to this specification in the presence of two witnesses.

PAUL E. SABINE.

lVitnesses:

FREDERICK F. MAsoN, EDITH OLSON. 

